Receiving apparatus



Filed July 8, 1950 Far/me EECEll/EK ATTORNEY Patented May 21, 1935 I UNITEDSTATES PATENT" OFFICET RECEIVING APPARATUS tion of Germany Application July 8, 1930, Serial No. 466,427

In Germany August 20, 1929 Claims. (01. '25os) ,When modulatinglkeyingl the amplitude of a shortwave transmitter in the usual way, it is frequently noticed at the receiving end that the signals seem extended, indeed,- the signals are longer and the spaces shorter than what has been sent out. Extensive investigations have shown that the beginning of the signal is always faithfully transmitted, but that after the completion of the transmitted signal additional energy arrives which presumably reaches the receiving station from the transmitter in a roundabout way and thus takes more time in arriving. If it is important to insure the correct length of the transmitted signals as is necessary, for instance,

: in picture telegraphy, then the signals must be chosen of greater length compared with the reverberation period in order that the latter may not become apparent. But this limitsthe rate of telegraphing. A

To increase the working speed it'has been suggested to modify the frequency of the transmitter in such a way that during the time the signal is transmitted one frequency is radiated off from the antenna; while during spaces a different frequency is radiated. The receiver must then be so conditioned that it will record only the beginnings of the wave-trains of each frequency. The signals will then be transmitted of the proper length independently of the reverberation period.

Receivers adapted to pick up detuned signals are known in the prior art. In what follows a receiving apparatus shall be disclosed which responds only to the beginning of incoming wavetrains and which makes a record of the signal from its beginning and the beginning of the space.

In the drawing, Fig. 1 shows the receiver arrangement, and Fig. 2 shows curves explanatory of the operation of the receiver.

The receiving means I and 2 of Fig. 1 comprise suitable signal absorption and rectifying devices and filter amplifiers adapted to separate the two frequencies fl and f2 from each other. According to this invention the signals of both frequencies are then separately rectified in rectifiers 3 and 4 connected with receivers I and 2 respectively, while after rectification they are fed to two transformers 5 and 6 whose impedance for the value for the beginning of the rectified signals is not small compared with the internal resistance of rectifiers 3 and 4. The output terminals of transformers 5 and 6 are associated with the grids of two additional tubes 1 and 8, and these are biased from biasing batteries 9 and Ill to an extent so that no plate current flows in the tubes when no signal is received.

The polarity of the transformers is so chosen that a growth of current in the primary winding results in positive charging of the grid connected to the secondary winding. When a signal of frequency fl reaches the receiver apparatus, a current starts to flow through the rectifier; while this current grows, a potential arises across the secondary winding of the transformer 5 whereby the action of biasing potential 9 is decreased. Hence, tube 1 furnishes a current. After the signal has been built up to its full value, the potential across transformer 5 collapses, and when the signal is terminated there arises there a'potential unidirectional with battery 8. Hence, it is only at the beginning of the. signal of frequency fl that tube 1 supplies a rush or impulse of current independently of the length of the signal. And in a similar way tube 8 furnishes an impulse of current only at the beginning of the'signal of frequency f2.

Connecting the tubes 1 and 8 with a relay comprising auxiliary sources of current or a similar a device I l in such a manner that an impulse from tube 1 shifts the relay in one position, and an impulse from tube 8 in the other direction, then currents will be derived from terminals l2, l3 which correspond to the signals to be transmitted without the latter being altered by reverberatinon phenomena; and the ensuing currents can be further treated and usedby recording appasolely upon the instant of the beginning, and not upon the duration or length of the signal in ques tion.

The whole process is schematically illustrated in the following manner (see Fig. 2)

I is the signal to be transmitted.

II amplitude of the incoming signals sent on frequency fl.

III amplitude of signals sent on frequency f2.

IV potential across terminals of transformer 5.

V potential across terminals of transformer 6.

VI and VII current from tubes 1., 8 respectively.

VIII current from terminals l2, l3.

Since the reverberation phenomena occasionally are not embraced by a smooth envelop, but present peaks occasioned by undesirable potentials across transformers 5 andli, it is recommendable to dispose means on either side of transformers and 6 which are permeable to signal frequencies-though impermeable for higher frequencies; or else the transformers themselves may be built so as to fulfill the identical end, as shown in Fig. 1 by capacities I4, l5, l6, M.

It may also be of advantage to so regulate the amplification factor that the amplification is greatly diminished upon the arrival of a signal while caused to rapidly grow after termination of a signal, the rate of growth being so chosen that after the reverberation period the sensitivity resumes its former value.

This normal amplification value in turn may be so controlled by the amplitude of the incoming signals that at such times when the signals come in very strong the amplification is made correspondingly small, and vice versa, so that the maximum value of the currents leaving rectifiers 3 and! will turn out roughly constant independently of the strength of the incoming signals.

1. The method of producing currents truly representative in electrical length to the marking and spacing impulses sent out at different frequencies by a transmitting system which includes the steps of, separately receiving said marking and spacing frequencies, rectifying each of said received frequencies to produce unidirectional currentimpulses, and producing by means of said unidirectional impulses a current flow whose initiation is. simultaneous with inception of said impulses but whose duration is independent of the length of said. impulses.

2. Means for receiving signals from a trans:

cmitter which sends out oscillations of one frequency for marking and oscillations of another frequency for spacing and for producing representations of time duration equal to the duration ofthe marking and spacing oscillations including, a separate receiving means for each of said frequencies, a rectifying means connected with each receiving means, a thermionic relay tube for each rectifying means, a transformer for each thermionic relay tube, each of said transformers having its primary winding connected with one of said rectifiers and its secondary winding connected with one of said relay tubes, a condenser connected in parallel to the secondary winding of each of said transformers, means for applying a constant biasing potential to the input electrodes of each of said thermionic relay tubes,

which biasing potential opposes the bias applied thereto when current flows in the vsecondary winding connected therewith, "and marking means connected with the output electrode of each of said relay tubes.

3. The method of producing currents truly representative in electrical length of the marking and spacing impulses sent out at different frequencies by a transmitting system which includes the steps of separately receiving said marking and spacing frequencies, rectifying each of said frequencies to produce unidirectional current impulses, utilizing the steep wave front only of the beginning of said unidirectional impulses to produce a current flow whose initiation is approxi- 'rnately simultaneous with the inception of said unidirectional impulses, but whose duration is shorter than the duration of said impulses.

4. The method of producing currents truly representative in electrical length of the marking and spacing impulses sent out at different frequencies by a transmitting system which includes the steps of separately receiving said marking and spacing frequencies rectifying each of said received frequencies to produce unidirectional current impulses, obtaining from each unidirectional impulse two sharp pulses of different polarities whose durations are independent of the length of said impulses, and utilizing only those sharpv impulses of a predetermined polarity to record the signal energy,

5. In a radio signaling system, the method of producing currents truly representative in electrical length of the marking and spacing impulses sent out at different frequencies by a transmitting system which includes the steps of separately receiving said marking and spacing frequencies, rectifying each of said received frequencies to produce unidirectional current impulses, obtaining from each unidirectional current impulse at the approximate inception thereof a sharp pulse of a predetermined polarity whose duration is independent of the length of said impulses, modifying said sharp pulses, and utilizing said sharp pulses of predetermined polarity to record the signal energy, the sharp pulses obtained from rectifying the marking frequencies recording the signal energy differently from those obtained from rectifying the spacing frequencies.

WILHELM RUNGE. 

